The present invention relates generally to an elevator system and, in particular, to a two-channel forked light barrier apparatus for the generation of car position information on the entry of a switching vane in the region of the door zones in elevator shafts for the purpose of the premature initiation of the opening of the doors on the arrival of the elevator car at a target floor.
The present invention concerns the premature initiation of the opening of the doors on the arrival of an elevator car at a target floor which sets high demands on equipment and circuits and which, within a door zone at the stopping position, bridges over the door and lock contacts in the final phase of the arriving elevator car. There exist regulations and standards which prescribe or recommend the function and a portion of the construction of such devices. Sub-assmblies, which meet these relevant safety regulations, are known as "fail-safe" devices. Generally, such apparatus have circuits which are constructed to be secure against failure in that a fault or a combination of faults cannot cause any dangerous state for the equipment to be controlled, in this case an elevator.
The European Patent Application No. 0357 888 describes a method and a device for the generation of elevator shaft position information by means of a safety light barrier. Test loops internal to the light barrier circuit monitor, statically in the rest position and dynamically during the travel of the elevator car on the entry and exit of the light barrier into or out of the actuating vanes in the shaft, the correct functioning of the circuit and, in the case of a fault, issue corresponding fault signals.
The U.S. Pat. No. 3,743,056 describes a fail-safe detector which has a failure-proof circuit and is protected particularly against external light and reflections.
Both of the above-described circuits have the disadvantage that a fault is discovered only when the corresponding function is used and the circuit is not constructed in a redundant fashion.